In many modern food retailing operations, such as in supermarkets, meat and produce markets and the like, there are customarily employed many types and sizes of food trays which are usually molded from wood or paper pulp or from various polymeric plastic materials, for instance, foamed plastic, for the display and packaging of meats, fish, poultry and other produce or comestibles.
In addition thereto, such trays may be frequently utilized in connection with the packaging and display of non-food products or commodities; for instance, items which may be sold in hardware stores, such as bolts and nuts, wrenches, screwdrivers and the like, amongst numerous others. Generally, these trays are relatively shallow rectangular flat-bottomed trays having outwardly inclined upstanding peripheral sidewalls, into which the commodities are placed, and thereafter a transparent heat-sealable material, such as a heat-shrinkable or stretchable plastic film, is tightly wrapped and sealed about the tray bottom so as to resultingly produce an attractive retail package. This type of package is extremely neat and aesthetically appealing to retail consumers, and concurrently forms a protective arrangement for the commodity contained therein while allowing prospective customers to view its contents, so as to greatly assist in the sale of the commodities.
To a considerable extent, the packaging of the commodities and subsequent sealing of the commodity-containing tray with the transparent overwrap film has usually been manually carried out by generally unskilled or semi-skilled labor. Although the packages obtained in this manner are, as a rule, satisfactory in their appearance and in the quality of sealing of the commodities, the procedure has been slow and cumbersome and not at all adapted to meeting high-volume production demands.
In recent decades, and at an ever increasing percentage of the total tray wrapping market, there have been developed automatic tray overwrap machines which, at high rates of speed, will wrap and seal a tray containing a commodity, such as meat, fish, poultry, vegetables, or the like comestibles, or non-food products, with a transparent overwrap film constituted of a suitable material of the kind mentioned hereinabove. Although the automatic overwrap machines to a large extent fulfill the demand for supplying wrapped trays of the type in question to a highly satisfactory degree, certain problems have been encountered in their use. Thus, the automatic overwrap machines, when positioning or contacting the trays for contact with the overwrap film, and during the sealing of the film to the trays, are prone to impart relatively high forces or bending loads to the sidewalls of the trays, thereby generating extremely high localized stesses which tend to frequently cause the side or end walls of the tray to buckle and/or fracture. This buckling may be the result of the inwardly directed forces exerted on the sidewalls of the tray due to impact by the machines and/or an outward bending force imparted to the sidewalls by the overwrap film which is being applied onto the commodity-containing trays.
Further basic causes of tray failure when the trays are overwrapped with transparent film in automatic machines may be ascribed to poor tray design for the intended applications thereof; in essence, inadequate sidewall and tray bottom strength; incorrect design criteria in the interrelationship between the tray bottom and the upright wall structures; design of automatic equipment and the like, amongst other factors.
In essence, the failures of packaging trays while being provided with an overwrap film enclosing the comestibles on the tray in automatic tray overwrap equipment may be primarily ascribed to one or more of the following:
1. Bending or breaking at the sidewall to tray bottom transitional radius due to a concentration of inwardly or outwardly directed bending moment stresses at this point in the tray.
2. Distortion, folding or breaking of the trim lip extending about the tray resulting from the large surface film contact area of the trim flange on the tray and the high coefficient of friction between the foamed plastic tray surface with the overwrap film surface.
3. Inadequate strength and resistance to buckling of the tray bottom wall resulting from the weight of the commodity in the tray and the forces exerted thereon by the overwrap film material.
4. Bowing and resultant buckling of the trays when subjected to the wrapping forces in the equipment, and the related package instability imparted thereto by the remainder of the automated weighing/pricing/labeling equipment.
Another significant problem which is encountered resides in providing the formation of an adequate seal between the surface of the tray bottom and the overwrap plastic film material as the product-containing packaging tray is conveyed through a sealing apparatus, such as heat sealer.
Occasionally, packaging trays are encountered which, due to various manufacturing or product-receiving reasons or the like, may possess a tray bottom structure with an outward or convex box rather than a flat surface. Consequently, the normally flat surface area of the tray bottom and the covering overwrap film material which is adapted to be contacted by the sealing apparatus about the perimeter of the tray bottom which is now slightly raised, is reduced by a considerable extent, and as a result, the sealing procedure is adversely affected so as to produce a relatively poor sealing contact between the tray bottom and the overwrap film material.
To some degree, the prior art has taken cognizance of the problems which are commnly encountered in the wrapping of trays with an overwrap film of the type described.
Holden U.S. Pat. No. 4,349,146, assigned to the common assignee of the present application, discloses a molded packaging tray for the packaging of comestibles, which possesses a reinforced peripheral lip structure extending about the upper ends of the tray sidewalls which will aid in preventing the collapse and fracture of the sidewalls caused by pressures exerted thereon by an overwrap film when applied thereto by an automatic tray overwrap machine.
Holden U.S. Pat. No. 4,442,969, also assigned to the common assignee of the present application, pertains to a novel reinforced molded packaging tray which, in addition to a strengthened peripheral lip structure encompassing the tray sidewalls, provides for the incorporation of integral stiffening rib structure in the bottom wall of the packaging tray. This will impart further strengthening against buckling to the packaging tray, which is of particular significance to larger-sized trays, commonly referred to as family pack trays.
Although the foregoing Holden U.S. Pat. Nos. 4,349,146 and 4,442,969 to a significant extent meet the needs of the industry with regard to the rapid and automated packaging of comestibles, such as meats, fish, poultry and the like, there is a need for the provision of packaging trays of this type which can satisfy the more stringent demands as to high strength which, for example, are frequently placed on the larger sized so-called family pack and other sizes of trays which contain larger amounts of and resultingly heavier quantities of the commodities. This is accomplished through the provision of a molded packaging tray, as described in Holden U.S. Pat. No. 4,623,088, also assigned to common assignee of the present application, which is adapted for use with an overwrap film in which the peripheral lip structure on the sidewalls of the tray is configured to minimize the surface contact with the overwrap film irrespective as to whether the commodity contained in the tray exceeds or is less than the overall interior height of the packaging tray. Pursuant to various embodiments of the packaging tray described therein, the tray also incorporates stiffening rib structure integrally formed in the basically flat bottom wall structure of the tray so as to still further enhance the overall strength of the packaging tray. Additionally, this patent discloses a packaging tray in which the central portion of the tray bottom is raised to some slight extent so as to provide for an increase in the pressure acting over the peripheral overwrap seal areas on the tray bottom.
The inventive meat or packaging tray improves upon the properties of the above-mentioned prior art trays through the provision of a crowned tray bottom, in which the crowned bottom portion, in the unloaded or empty unweighted state of the tray, is raised to a height which is at least a substantial proportion of the total overall height of the tray, or in which the crowned portion may even extend the full height thereof, and wherein a preferably thickened side radius joins the periphery of the tray bottom to form a transition to the sidewalls of the tray so as to considerably increase the resistance of the tray to buckling and deformation loads and stresses.